1. Field of the Invention
The present invention relates to a novel strain of the fungus Colletotrichum gloeosporioides possessing herbicidal activity against sicklepod and coffee senna which are weeds endemic to the southern United States, and methods for its use.
2. Description of the Prior Art
Sicklepod (Cassia obtusifolia L.) is a major weed problem in much of the southern United States where soybeans and peanuts are grown. This non-nodulating legume is very competitive with these crop plants and can significantly reduce yields at low weed densities. Mature sicklepod plants commonly reach a height of 2 to 2.5 m. The weed produces large quantities of seeds that can germinate and grow under a wide range of environmental conditions. Seedlings characteristically have rounded cotyledons, 15-20 mm across, with 3 to 5 distinct yeins in the upper leaf surface. The first leaves have 3-5 leaflets that are rounded at the tip.
Sicklepod control with herbicides is difficult. An emergency use permit has previously been issued by the United States Environmental Protection Agency (EPA) to allow the use of toxaphene for sicklepod control in soybeans grown in several southern states. Also, metribuzin has been allowed to be applied postmergence directed, but this chemical is sometimes injurious to the soybeans.
Coffee senna (Cassia occidentalis L.) is similar in appearance to sicklepod, except that the seed pods are shorter, straighter, and more flattened. It is a non-nodulating leguminous weed in soybean, cotton, and peanut fields in much of the southeastern United States. Although originally introduced as a potential crop, it has escaped cultivation and has become a weed pest. It causes yield loss, seed quality degradation, and difficulty with harvest (Brown et al.; Proc. South. Weed Sci. Soc. 42:111; 1989). Control is difficult because of its tolerance to many commonly used herbicides, its prolific growth habit and season-long emergence (Elmore; Proc. South. Weed Sci. Soc. 42:408-420; 1989).
The practicality of mycoherbicides for the control of various weeds has been established. U.S. Pat. No. 3,849,104 (Daniel et al.) disclose the control of northern jointvetch with Colletotrichum gloeosporioides (Penz.) f. sp. aeschynomene (ATCC 20358). Another strain of this fungus, Colletotrichum gloeosporioides (Penz.) f. sp. jussiaeae (ATCC 52634) has been used to control primrose (Boyette, Weed Science, 27: 497-501).
Walker in U.S. Pat. No. 4,390,360 discloses methods for the biological control of multiple weed plants including sicklepod, showy crotalaria, and coffee senna. Control is accomplished by use of a specific host strain of the fungus Alternaria cassiae (NRRC 12553) to produce lesions in and kill weeds of these species.